DENVER (AP) — Air quality alerts were posted on Sunday for numerous areas of the U.S. West and Midwest as wildfire smoke continues to linger over much of the country. The alerts came across the northern U.S. Rockies, including portions of Colorado, Wyoming, Washington state and Idaho. Further to the east, smoke from fires burning in Canada  was drifting for hundreds of miles and triggering pollution alerts in Wisconsin, Minnesota and Iowa. Wildfires emit huge volumes of microscopic smoke particles that researchers say can  be harmful if breathed in, leading to both immediate and long-term health impacts. Children, the elderly and people with underlying health conditions are particularly at risk.